What does the 0x80 port address connect to?

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When sending a command and reading the data from a certain chip, say the RTC, different documents say that we should wait for some time before reading from the device to make sure the data is available. Many pieces of code make a dummy read from the port 0x80. I wanted to know to what device this address location is connected, if any. I am talking with respect to the IA-32 PC architecture.

hardware port x86 io
3 Answers

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You can write (and read) to (from) port 0x80 by using this code in a kernel driver:

(Note that some PCs like mine have a WORD at this location so one can write 16 bits to it.)

Windows driver example:
__outword(0x80, 0x00A0);

This may also be used for kernel debug in cases where you do not have a two machine debug system and you can't use debugview traces for any reason (like the system freezes). Port 80 may be keeping your last debug code for you.

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